What is the best way to inexpensively vapor barrier a wall?
...wall currently is, and why you're asking. Is there a mold issue? Is it a basement or an above grade wall? How old is the home? And what is the current wall assembly, is it a stud frame wall with batt insulation and any membranes? I'm assuming it has no vapor barrier if you're asking, so fill us in a bit with what you'v...